Why active suspension won’t solve F1's porpoising problem

Racing tech

As F1 teams struggle to eliminate the high-speed bouncing suffered by this year's cars, active suspension seems like an obvious solution. But it's not, writes Lawrence Butcher

Alain Prost in 1993 Williams FW15 F1 car

Prost found it difficult to adjust to the '93 Williams, but still said the car was very special to him

Grand Prix Photo

Author

Lawrence Butcher

There has been much talk about ‘porpoising’ over the course of pre-season testing, with the phenomenon seemingly coming as a surprise to teams. Cars that generate the bulk of their downforce from the underfloor can be prone to the problem, and in other series such as WEC, it is something that engineers have had to contend with for years.

As F1’s chief technical officer Pat Symonds commented during the first test: “Anyone who has worked in sports cars knows the phenomenon and anyone who has been in F1 for a long time knows about it. It’s fixable. The secret, as it always has been, [is] to minimise the instability while keeping the performance.”

It is this second point that teams appeared to be working intently on during the second test, figuring out the careful balance between ride height and stiffness that would allow them to maximise downforce without turning the car into an angry pogo stick.

The problem is that while the ideal ride height – which places the floor at the optimum distance from the track for maximum downforce generation – might be fine around the bulk of any track, on the straights the increased downforce will invariably push the car too low, stalling the aero and initiating the porpoising. If the frequency of this push-pull action happens to be in the same region as the chassis natural frequency, things get really fruity for the driver. (The natural frequency is that which the sprung mass of the car would ‘vibrate’ at if there was no damping applied to the suspension.)

Heading off on a slight tangent, it is potentially possible that when porpoising occurs in sync with the natural frequency of the suspension, the dampers are simply overcome. Oddly enough, a different but relatable issue has seen the adoption of technology originated in F1 in the world of Pro Stock drag racing. There, the cars can suffer from a phenomenon known as tyre shake, where the rear tyres slip then grip very quickly, setting up an oscillation in the tyre that grows and grows. In recent years, teams have started to use dampers with integrated inerters which have all but cured the problem. These contain a plunger that slides in and out as the car moves up and down, causing a flywheel to rotate which stores energy. This helps to control the very high frequency tyre oscillations which occur beyond the frequencies regular dampers can handle.

2017 Ferrari F1 suspension with inerter

Inerters helped to reduce oscillations but are banned for this year

Grand Prix Photo

No doubt if F1 teams were still permitted the various interlinked suspension systems and interters used in previous years (or even Renault’s tuned mass damper), it would be easier to get on top of the problem, but they are not, and have only traditional springs and dampers to work with.

Of course, they could just run the ideal ride height with very high spring rates to prevent the floor bottoming out, but this in turn will lead to a deficit in performance where suspension compliance is needed. What they are left with is having to work through various combinations of ride heights, spring rates and damper settings to find a compromise that they can live with. Hence why testing is so important as the data gathered in Bahrain and Barcelona will be used to modify their vehicle simulation models and, they hope, allow them to come up with combinations that will work at other circuits.

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The particular aero development path each team has chosen will also impact how effectively they can counter the problem. Those that have designs optimised to run as close to the ground as possible will likely have more issues that those who have pursued a path of slightly higher ride heights and greater use of airflow off the side of the floor to seal the underside.

Of course, active suspension, which effectively allows for the ride height of the car to be set regardless of bump compliance and other factors would make the problem go away, as suggested by Mercedes’ George Russell.

The idea of a ‘spec’ active system for F1 was discussed in FIA working groups a couple of years ago, but dismissed in favour of greatly simplified passive systems. While it is easy to say, ok, everyone run this standard system, in practice, development would take time and no single solution could be bolted into every car. Each team (with the possible exception of those who have chosen the customer route to suspension components) will have their own damper designs, as well as very different mounting points, rockers and suspension motion ratios. Not to mention Red Bull and McLaren with their pull rod front set-ups. All of which are intrinsically tied to the packaging of their cars. Any active system would also need its own bespoke control electronics, which again opens the can of worms around how far teams can go with coding and developing their own software.

This would mean, as pointed out by various technical directors including McLaren’s James Key and AlphaTauri’s Jody Egginton, not insubstantial costs and a prolonged development process. Any such system would be at least one, and more likely two years in the making, by which point, the combined brain trusts of each team will have likely come up with passive solutions. One then has the fact that even spec active suspension would invariably lead to much faster lap times, with knock on effects in terms of tyre performance and even (if things got really out of hand) track safety limits. No doubt teams would love to have the flexibility of active control, but their attentions and resources will be all be dedicated to the tools they currently have. As Key summed up, “As a technical director, I’d love to see the return of active suspension personally. But, with the cost cap, it’s not the best project to be doing.”

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